What epoxy stands up to sunlight?

What you need is epoxy additive, they sell them in many places, I bought some at raka.com a while ago.

Anything with the word "marine" in it will probably work.

Not true, but I have delt with Raka for epoxy before. He may have something, but his mixes are good for penetrating wood. Epoxy in general does not fair well in sunlight. They usually paint the epoxy with poly urethane in marine applications. Its been a few years since I researched epoxies, and things change. This looks promising...

Cheers

On Sat, 23 Dec 2006 03:17:11 GMT, "Martin Riddle" Gave us:

Depends on the epoxy.

There are many surface coatings that are epoxy based specifically for their longevity.

Not every epoxy behaves like 5 minute epoxy.

Need a two part clear weather proof epoxy. Any recommendations?

Want it to last for 3-5 years and not yellow or erode.

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--------------------- Maybe check any nearby commercial/industrial paint stores and see what they got or can get. You might have to buy 1 gallon minimun. I've heard of 2 part clear urethane. Could be a substitute. D

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I don't think any will last more than 12-18 months without some sort of additive or overcoat.

System Three has one with UV protection designed in, it's known as SB-112. West Systems' application note says that aluminium powder gives limited protection. But most recommend a polyurethane coat, which is basically sacrificial (like all paints) and requires re-coating now and then. For instance, System Three recommends their WR-LPU Linear Polyurethane Topcoat

Barry Lennox wrote in news: snipped-for-privacy@4ax.com:

S3's Epoxy Book is well worth the download time. A good source of info on epoxies.

Thanks for the feedback.

They claim LEDs are epoxy and they seem able to stand up to sunlight - but they probably aren't just 2 part epoxy.

I'm trying to avoid the paint coating. What I'm doing is potting the circuit board in epoxy and want the LEDs to stand up out of the potting compound.

And - I'd like to play with it and see how the refractive index of a non-yellowing epoxy changes the beam spread of the diodes - that may give me some ideas on outdoor lighting with LEDs

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On Sat, 23 Dec 2006 05:46:43 GMT, snipped-for-privacy@comic.com (D from BC) Gave us:

Not enough information.

Epoxies can be flexible to brittle, cohesive or adhesive

You need to describe what is being "epoxied". Is it being subjected to physical stresses as in is it a structural need like holding a piece perpendicular to another?

Is it merely being used as a hole filler or spackling or weather seal?

For structural uses, you don't want brittle. You may want to add glass or carbon filaments to the mix prior to application in such instances.

There are a lot of factor so you should give a bit more info as to what you wish to bond.

On Sat, 23 Dec 2006 10:52:48 -0500, default Gave us:

Epoxy, by definition, is two part.

On Sat, 23 Dec 2006 10:52:48 -0500, default Gave us:

Instead of immersing them, use opaque epoxies and leave the LED tops exposed. You would get the as design maximum optical output from them that way.

recommendations?

Thanks for the feedback.

They claim LEDs are epoxy and they seem able to stand up to sunlight - but they probably aren't just 2 part epoxy.

I'm trying to avoid the paint coating. What I'm doing is potting the circuit board in epoxy and want the LEDs to stand up out of the potting compound.

And - I'd like to play with it and see how the refractive index of a non-yellowing epoxy changes the beam spread of the diodes - that may give me some ideas on outdoor lighting with LEDs

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-------------- Got one more suggestion for verification.... I recall looking into 2 part epoxy for floors long ago. Use example: Industrial buildings and restaurant floors.. That might be an example of something that should be designed to resist yellowing. (Or tinted so the yellowing is not obvious) Goofy... One time I did potting with non-pure epoxy paint...I was told it doesn't dry due to solvent entrapment. After 1 month of drying, I was able to snap my brick like an granola bar :( D

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Are you sure? Can't have heat, air or UV curing epoxy, for instance?

I've seen paints that claim they contain "epoxy resins," and are one part paints (and yes, some are two part)

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That is what I've been doing. There's a little bit of light lost to the tinted epoxy - still erodes and looks like s*it after a time.

Doubtless a more die hard pigment or more of it would help.

Metal powders work OK, providing one really loads up the epoxy with the powder then buffs off the top layer of pure resin to expose the metal - not practical for lights, but a pleasant and good wearing surface.

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I've been making outdoor lights,sometimes with a touch of electronics thrown in - ambient light sensing via CdS cells, differential light sensing, timers, etc.. CDS cells don't take kindly to moisture and need to see light. (OK I could get hermetically sealed metal and glass ones - they cost - or stick a photo transistor out of the epoxy

- but I'd like to have just a foolproof, bullet-proof, all weather, "brick" with wires coming out).

Basically a potting compound with some structural strength - but not as hard as glass and UV resistant, and crystal clear is desirable.

I like some of the effects one can achieve by immersing the LEDs under the potting then controlling the shape of the mounting plane or circuit board and controlling the shape of the cured epoxy. So I really want the stuff to be clear and withstand sunlight. This would open up some new ideas and applications - you know, fun stuff.

It may be that epoxy isn't the ideal stuff to use - it's just what I have been playing with. Polyester resin has problems too - Vinyl ester is showing some promise, but it is too soon to tell. Haven't found any good polyurethane either - the UV poly looks bluish and tends to fluoresce slightly so I can't drop white or blue leds down in it - and the refractive index is low.

I'm trying to see what can be done . . rather than a fixed, specific application.

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On Sat, 23 Dec 2006 14:18:30 -0500, default Gave us:

If it is an epoxy, it is two parts that get mixed, regardless of the curing function/method. There are ingredients that get added to epoxies that give it other properties such as thermal conductivity, shear resistance, etc. Theses are glass filled, and ceramic filled versions.

An epoxy is an epoxy, but a paint that has epoxy like features is a paint.

An epoxy usually refers to bonding of structural elements, not surface coatings.

A potting compound should be pliable to keep from shearing components or connections during thermal cycling. Hard potting compounds are typically bad for circuits. Use softer RTV compounds for that, or a good Polyurethane, though that is very expensive.

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On Sat, 23 Dec 2006 14:26:26 -0500, default Gave us:

Obviously not. READ WHAT I SAID. INSTEAD of immersing them. That means that they do NOT get ANY material added to their optical output area.

Not if they are OUTSIDE the epoxy.

If I recall you were after CLEAR epoxy. There would be NO pigment in it. Sheesh.

You're a strange animal.

Basically, all epoxies are two part. Some 'epoxy paints', are two part systems, where the second part is added at the paint store, with a limited shelf life from this point (my local shop does these with 24 hour, and 7 day curing times). However some paints sold as 'epoxy', are not, but have 'epoxy like' performance/behaviour (beware marketting...). Cycloaliphatic epoxies are better for UV resistance. The epoxies used for LED encapsulation, are high temperature cured, and have different chemical structures from the room temperature chemistries. Most use something like 150C for the cure cycle... I'd suggest looking for HDMI polyurethanes, or even better an acrylic resin. The molecular structure here is much better able to resist UV degradation (hence the relatively good performance of acrylics like Perspex). However the best solution is a UV blocking additive. Modifying your design so that an opaque agent will be acceptable, is probably the 'best' solution.

Best Wishes

Exactly; either black epoxy, or add coloring (preferably black), or an anti-oxidant (limited protection), or coat the outside with black paint.